Attorneys for an Arizona inmate who may be sentenced to death for killing an Oklahoma couple following a prison break may launch a mental health defense during the sentencing phase of his trial.

The defense filed a motion in federal court Tuesday afternoon saying it intends to introduce evidence about John McCluskey's state of mind.

McCluskey was convicted Monday on 20 counts stemming from the carjacking and murders of Gary and Linda Haas. The retired couple from Tecumseh, Okla., was killed in 2010 in New Mexico after crossing paths with McCluskey, his girlfriend and his prison bunkmate following their escape from an Arizona prison.

The Albuquerque jury that convicted McCluskey will decide whether he should be sentenced to death or life in prison. The penalty phase is expected to take weeks.